Praeaphanostoma gusana, Hooge & Eppinger, 2005

Hooge, Matthew D. & Eppinger, Neil, 2005, New species of Acoela (Acoelomorpha) from the Gulf of California, Zootaxa 1009 (1), pp. 1-14 : 10-13

Praeaphanostoma gusana sp. nov. (Figs. 7,8)

Type Material. Holotype. AMNH PLATY 1664 , set of 1.5­µm­thick serial sagittal sections of epoxy­embedded specimen stained with toluidine blue . Paratype. AMNH PLATY 1665 , set of 1.5­µm­thick serial sagittal sections of epoxy­embedded specimen stained with toluidine blue .

Type Locality. San Felipe, Baja California, from intertidal fine sand from the northwest corner of San Felipe Bay (31°01’03.4” N, 114°49’50.3” W) .

Other Material Examined. Photographs of living specimens in squeeze preparations, and one set of 1.5­µm­thick serial sagittal sections of epoxy­embedded specimen.

Etymology. Species name is a derivation of the Spanish gusano, worm.

Description. Mature, living specimens ~ 400 µm long and ~ 150 µm wide ( Figs. 7A , 8A, B ). Preserved specimens contracted to ~ 260 µm long. Anterior and posterior ends rounded. Body cylindrical.

Epidermis completely ciliated. Rhabdoid glands present. Body colorless in transmitted light, but digestive syncytium with yellow coloration.

Frontal organ well developed. Cell bodies of frontal glands positioned ~ 110 µm behind frontal pore ( Fig. 7B ).

Mouth opening on ventral surface, middle of body. Digestive central syncytium extends from frontal glands posteriorly to male copulatory apparatus.

Ovaries paired, ventral; extend from frontal glands posteriorly to seminal bursa ( Figs. 7A, B ).

Testes paired, lateral to eggs; separate from ovary. Testes extend from frontal gland posteriorly to level of seminal bursa ( Figs. 7A, B ).

Common gonopore opens anteriorly to vagina and posteriorly to male copulatory apparatus ( Figs. 7A , 8C ).

Narrow vagina extends anteriorly along posterior side of seminal vesicle; opens to seminal bursa ( Figs. 7B , 8C ). Seminal bursa with well­defined bursa wall. Bursa filled with sperm in living specimens, but sperm absent in fixed specimens ( Fig. 8C ). Bursa without bursal appendage.

Gonopore opens directly to well­developed, curved penis with outer longitudinal muscles and inner circular muscles ( Figs. 7B , 8C ). Tip of penis with a cluster of granules (Kornsekret, sensu Dörjes 1968). Penis invaginated into muscular seminal vesicle filled with sperm clustered to anterior side of penis.

Remarks. The genus Praeaphanostoma is composed of 10 species that can be distinguished from other members of the Isodiametridae by their possession of a walled seminal bursa that lacks an appendage such as a bursal nozzle, and their lack of eyespots (as found in Ancylocirrus ), or a long tubular, ciliated vagina (as found in Bursosaphia ). Praeaphanostoma gusana has a single gonopore, a slightly curved penis with granules clustered at the tip of the lumen, and is without a sphincter on the vagina. While all of these are common features in this genus, no other member of Praeaphanostoma has this exact suite of characters.

Figures

FIGURE 7. Praeaphanostoma gusana sp. nov.; reconstructions to show arrangement of organs. A. Dorsal reconstruction of whole organism. B. Sagittal reconstruction of whole organism. cs, digestive central syncytium; e, egg; fg, frontal gland; gp, gonopore; gr, granules; m, mouth; p, penis; rh, rhabdoid gland; sb, seminal bursa; st, statocyst; sv, seminal vesicle; t, testes; v, vagina.

FIGURE 8. Praeaphanostoma gusana sp. nov.; photomicrographs. A. Dorsal view of living specimen. B. Dorsal view of posterior. C. Sagittal histological section of copulatory organs. gp, gonopore; gr, granules; p, penis; sb, seminal bursa; sv, seminal vesicle.